A solar cell module, which converts the light energy from the sun to electrical energy, attracts attention as a clean energy source capable of generating electricity without emitting carbon dioxide to cope with environmental issues, such as air pollution and global warming.
In general, a solar cell module is configured of: solar cells, comprised of crystal silicon, amorphous silicon or the like, to perform photoelectric conversion; an encapsulant (filling layer), comprised of an electrical insulator, to encapsulate the solar cells; a front surface protective sheet (front sheet) laminated on the front surface of the encapsulant (light receiving surface); and a back surface protective sheet (back sheet) laminated on the back surface of the encapsulant. In order for the solar cell module to have weatherability and durability sustainable for long period of time in outdoor and indoor use, it is required to protect the solar cells and the encapsulant from weather, humidity, fugitive dust, mechanical impact and the like, and avoid the interior of the solar cell module from exposure to the external air thereby to keep hermetically closed state. In this respect, a protective sheet for solar cells is required to have weatherability and durability sustainable for long period use.
Patent Document 1 discloses a back surface protective sheet for solar cells in which an inorganic oxide layer, an adhesive layer and a thermoplastic resin layer are laminated in this order on one surface of a film. This back surface protective sheet for solar cells is applied, via the thermoplastic resin layer, to the encapsulant by being heated and pressed thereon. The film comprises a resin, such as polyethylene terephthalate, on which silicon oxide layer or the like is vacuum-deposited as an inorganic oxide layer. The adhesive layer comprises a maleic acid anhydride modified polyethylene resin while the thermoplastic resin layer comprises polypropylene or the like, and the adhesive layer and the thermoplastic resin layer are laminated on the film with the inorganic oxide layer (a base material) by means of a multilayer co-extrusion lamination method.